Thermal behavior and electrochemical properties of propylene carbonate (PC) plasticized polyelectrolyte based on poly[lithium-N(4-sulfophenyl) maleimide-co-methoxy oligo(oxyethylene) methacrylate] have been investigated. This PC plasticized polyelectrolyte with a PC content of 54.5 wt% has an ionic conductivity of 1.8 x 10(-5) S cm(-1) at ambient temperature and a wide electrochemical window. Passivation phenomena occurring at the interface between the PC plasticized polyelectrolyte and a Li electrode were particularly evaluated and discussed.